In general, an inkjet ink is an aqueous ink, and water-soluble materials are used. In recent years, an erasable inkjet ink including a leuco dye, a developer, and a solvent has been proposed. By using such an inkjet ink, a high density image can be formed on a paper, and the obtained image can be erased with heat. By heating the paper where the image has been formed, the image is erased and becomes invisible.
In addition to having the characteristics of an erasable ink, the erasable inkjet ink is also required to have the characteristics of an inject ink, such as the ejection performance from a printhead. All characteristics are required to be maintained without degradation with time. A combination of water and an alcohol may be used as the solvent of inkjet ink, and it needs to be prescribed appropriately so as to satisfy the above-mentioned characteristics.